For various applications, more particularly for large-size anti-friction bearings employed in off-shore applications, with cranes or buoys it is purposive to provide testing appliances which, working in non-destructive manner and without requiring a disassembly of the bearing, are capable of detecting cracks at the race and/or adjacent regions of the bearing rings. With a prior art device of the initially designated species (EP 0 529 354 B1), detecting and monitoring of damage to races or the like is accomplished by the aid of a measuring device arranged in the anti-friction bearing chamber and having sensors supplied with operating energy in contact-less manner from the outside by way of inductive means. For this purpose, a first coil acting as energy source is arranged in the anti-friction bearing chamber to supply the required electrical energy to the measuring device, whereas an induction coil connectible to an exterior power net and inductively coupled to the first coil is provided in one of the bearing rings, said induction coil being located in a circumferential groove open towards the anti-friction bearing chamber and extending over the entire bearing circumference. A uniform and even transfer of energy to the first coil is thus made possible irrespective of the momentary position of the bearing rings.
However, such devices are considered expensive in that the circumferential groove destined to accommodate the induction coil must be configured in the mostly hardened area of the relevant bearing ring, the area facing the anti-friction bearing chamber. In case the bearings are of a type that does not permit two complete revolutions in one direction or another during the measurement, but still call for monitoring the complete bearing rings, it is necessary to provide for several measuring devices. To avoid reciprocal interferences on transmission of data, it is expedient to provide a number of induction coils and a corresponding number of circumferential grooves that corresponds to the number of measuring devices, which multiplies expenditure and cost involved. Irrespective thereof, it is only possible to accommodate a maximum of two induction coils for lack of space, thus entailing restrictions with regard to measuring possibilities.